Telescoping boom



March 15, 1960 s. K. CLEMENTS TELESCOPING BOOM Filed Feb. 10, 1955 United Sttes Patent 2,928,493 TELESCOPING BOOM Shannon K.'lements, Elkhart, Ind., assiguor of one-half to Hugh M. Rush, Elkhart, Ind.

Application February 10, 1955, Serial No. 487,267

17 Claims. (Cl. 182-2) This invention pertains to load handling booms, and relates particularly to a novel construction of a telescoping boom for supporting a work station at elevated positions above the ground.

It is a principal object of the present invention to provide a telescoping boom for supporting a work station in horizontal position, regardless of the angular inclination of the boom and the degree of extension of the boom.

' Another important object of this invetnion is the provision of a telescoping boom in which the terminal end is adapted to move along a plane normal to the plane of the underlying support, as the boom is rotated on an axis parallel to said underlying support.

A further important object of this invention is to provide a telescoping boom wherein the mechanism effecting the extension and retraction of the boom is enclosed within the latter.

Still another important object of the present invention is to provide a telescoping boom for supporting a work station, and wherein the operation of the boom may be controlled from the remote position of said work station.

A still further object of this invention is to provide a telescoping boom which is rugged in construction to accommodate heavy usage and which requires a minimum amount of skill and effort for operation, maintenance and repair.

These and other objects and advantages of the present invention will appear from the following detailed description, taken in connection with the accompanying drawing, in which:

Figure l is a fragmentary foreshortened view in side elevation showing a telescoping boom embodying the features of the present invention, parts thereof being broken away to disclose details of construction;

Figure 2 is a sectional view taken along the line 2-2 in Figure l; and V Figure 3 is a fragmentary foreshortened view in side elevation showing a modified form of telescoping boom construction embodying the features of the present invention.

Referring to Figure '1 of the drawing, the boom assembly illustrated includes a forward boom section mounted slidably Within the'rearward boom section 11. As best shown in Figure 2, these sections are preferably of rectangular or other non-circular cross section so as to prevent the sections from rotating axially with respect to each other.

the outer rearward section 11, as previously explained, and the extent of rearward movement of the end section 10 is limited by such means as a stop 18 provided adjacent the rearward end of the outer section 11 for abutment by the rearward end of the inner section.

The top plate of the outer section 11 preferably is formed with a longitudinal upward offset section 19 which functions as a cable guide in the manner more fully explained hereinafter.

An elongated post 20 is secured at its rearward end to a bracket 21 secured between the side walls 14 of the housing described above. The post 20 extends forwardly to a point adjacent the forward end of the outer boom section 11, within the hollow inner section 10, and is provided at its forward end with a pulley 22, which is mounted rotatably on shaft 23.

Also mounted within the housing rearwardly of the bracket 21 is a cable drum 25 which is mounted for rotation on shaft 26 supported between the side walls 14.

A cable 27 is wound about the drum 25. One end of the cable is secured to a clamp 28 mounted adjacent the rear- The rearward section 11 is secured to or otherwise ward end of the inner boom section 10. The other end of the cable is first reeved over pulley 22 and then secured to the clamp 28, as indicated." Thus, it will be under -v stood that as the drum 25 is rotated in a counterclockwise direction, the lower strand of cable 27 will be wound upon it and theupper strand of cable will be unwound from it. It will be understood that cable 27 may be provided as two separate sections, each secured at one end to the drum and at the opposite end to thelclamp 28.

Since the lower strand of cable is reeved over pulley 22 and thence connected to clamp 28, it will be seen that this rotation of drum 25 causes the inner boom section it) to. be extended outwardly with respect to the rearward section 11. Reverse rotation of drum 25 results in retraction of the boom section 10, as will be apparent.

Rotation of drum 2.5 is effected by means of drive motor 30 which is shown to be connected tothe drum through a chain of gears. The system illustrated is simply a con venience in separating the parts to clarify the disclosure, and in actual practice may be simplified as explained hereinafter. However, as illustrated, the drive shaft 31 of motor 30 carries a worm 32 which meshes with worm wheel 33 mounted on shaft 34 which is supported between the side plates 14 of the housing. Worm wheel 33, in turn, meshes with worm wheel 35 whichissecured to drum 25.

At the forward end of the inner telescoping boom section 10 is a work station'37, preferably constructed in the form of a cage having an open top and a platform adapted to support thereon one or more workmen. The work station 37 is pivotally secured to the boom section 1% by pivot shaft 38. In the construction illustrated, the work station 37 is pivotally attached to the boom adjacent the lower rearward edge, whereby the weight of'the work station tends to rotate itself in a counterclockwise direction about the pivot point 38. Thus, to support said work station against free rotation, the forward end of cable 39 is secured thereto by means of pin 49. The cable extends rearwardly under guide pulley 41 which is mounted rotatably on a bracket secured adjacent the forward end of boom section it The cable then extends through'the cable guide 19 into the rearward housing, where it is reeved over pulley 42 which is mounted for rotation on a shaft extending between the side plates 14. Cable 39 then extends'downwardly and is reeved about pulley 43 which is mountedfor rotation on shaft 44 securedfto bracket 45 attached to the main support post.17.

From pulley 4-3, cable 39 extends upwardly and is wound about drum 46 which is secured to worm wheel 33. It' will be understood that cable 39 may, in practice, be returned-to a second section of drum 25, rather than't'o the separate'drurn 46, whereby to eliminate the elements 33, 34, 46. 'The additional assembly is illustrated in the drawings merely to separate the cables 27, 39, for .easeof understanding. It is to be pointed out here that th'erefexi'sts acritical relationship between the distances separating the pivot points 38, 40. and .the'distances separating pulleys 42, 43 and drum 46 and pulley 43. As the boom is pivoted about pivotpin 16 to varying degrees of inclination, the distances of pulley 42 and drum 46 from pulley 43 vary.

4 inbefore, the workmen enter the work station 37 by manipulating the boom to bring the station close to the ground. Then, if it is desired to rotate the boom in clockwise direction about pivot 16, to elevate the station, the operator pressestheproper pushbutton 61 controlling the forward rotation of motor 50. Thereupon cable drum 55 is caused to rotate in counterclockwise direction, and the windingin of cable results in the Thus, for example, as the. boom is pivoted in a clockwise direction about pivot pin 16', pulley 42and drum 46 move closer to pulley 43, thereby letting slack come into cable 39 in. the stretches extending between these elements. Hence, it is necessary that the forward end of cable 39 be connected at a point 40 which is located with respect to pivot 38 insuch manner that the amount of slack previously mentioned is equal to the amount of additional length of cable needed at the forward end to permit the required. angular displacement between the floorof the work station 37 and the boom 10 to maintain the work station in a horizontal plane. By proper selection of these points, the boom assembly may be pivoted through a wide angle and the floor of'the work station 37 is maintained horizontal at all times.

Inthe embodiment illustrated, the boom sections 10,

11 are :pivoted about pivot 16 by means of motor 50,

the drive shaftSl of which carries worm 52 which meshes with worm wheel 53. This wheel is mounted on shaft 54 supported between the side walls 14. .Cable drum 55.is secured to worm wheel 53.: .Cable 56 is wound upon the .drum 55, with one end. of the cable secured thereto. The, opposite end of thecable is reeved over pulley 57 mounted for rotation on' pivot pin 58 secured to the bracket 45,.and said end ofvth e cable 56 is then,

secured to a side wall 14 by .anchor pin 59. 1 It will be understood that variousYother forms of power systems may be employed to pivot the boom on support 17.

The motors and 50.are preferably electric, although they maybe hydraulic or any other type desired. In any case, it is-desirable that these motors be controlled from the work station 37. i To this end, and with the use of electric motors, there .is provided at the'work station 37 a control box 60 which includes a plurality of push button electric switches 61; These switches are each connected through flexible electric conductors (notshown) to the respective forward and reverse electrical circuits of said motors, in manner well-known to those skilled in the art. Y i f It is further desirable that the motors 30 and-50 be controllable from a point on the ground,'in the event that accidents or other circumstance affecting the workmen in the work station 37 prevents their manipulation of the boom assembly. Accordingly, there-may be provided a second control box.62, mounted, for example, on the main support post 17 .and provided with similar push button electric switches 63, each of which maybe desired rotation of the boom.

As the'boom is pivoted in clockwise direction, pulley 42 and drum 46 are moved closer to pulley 43 and the slackresulting inthe immediate stretches of cable 39 is paid out between pulley 42 and connecting pin to maintain the floor of the work. station 37 in a horizontal plane. It is assumed, ofcourse, tha'tthe vehicle or other support on which the post 17 is mounted also rests on the horizontal surface, or alternatively that the supporting post 17- has beenadjusted to extend in.a vertical plane. Under either of these conditions the platform of work station 37 will remain horizontal, which is parallel to the ground support and normal to the. axisof post 17. i a

Now, if it is desired to extend the forward section 10, the operator presses theproper pushbutton 61 to energize motor 30' in itsforward direction. Thus, drum 45 caused torotate in counterclockwise direction to extend the boom section 10,. aspreviously explained. Simultaneously therewith, drum.46 is caused to rotate in clockwise direction, whereupon cable 39 is unwound from connected in parallel with its corresponding switch in V said drum. Since drums 25 and 46 are of equal diameter, .it will be understood that simultaneous rotation of the drums causes cable 39 to be unwound. from drum 46 in an amount equal to the amount of. cable 27 being wound upon drum 25. Thus, the length of cable 39 is unwound fromdrum 46 to equal the lengthof extension of boom section 10. xln this manner, the horizontal position of workstation 37 is maintained as the boom section 10 is extended orretracted. In certain types of use of "a boom carrying a work station, it is desirable'to move the work station to various positions along a vertical plane. .Such operation is ad- ;vantageous, for example, when the boom and work, station assembly is employed to carry painters for painting the vertical walls of buildings. Thus, it is desirable that the work station be adjustable from one control to change the angleof inclination of the boom and yet maintain the work station adjacent said vertical plane, Accordingly, the modified construction of Figure 3 is provided to adjust automatically the degree of extension of boom section 10 as theboom assembly is pivoted about pivot pin 16, so that the .work station 37 will follow a vertical plane.

The general construction of the boom assembly shown in-Figure 3 is similar to the construction shown in Figure 1. described hereinbefore. ,Similar elements of construe:

tion are identified in' both views bythe samereference tation on shaft 67 carried by bracket 45. Y The cable then speed of counterclockwise rotation of the boom about 1 pivot16. Various types of shock absorber devices or extends upwardly over, pulley 68 rotatably mounted on side plate 14, and thence to cable clamp 28 where it is secured firmly to the rearward end of boom section 10. The cable then extends forwardly over pulley 22 and then rearwardly over pulley 69 mounted rotatably on side plate 14. From pulley 69 the cable extends forwardly over pulley 70 mounted rotatably on the downward projection 15 and thence under pulley 71- mounted rotatably on bracket 72 securedto the main support post 17. Cable 27 thenextends upwardly over pulley 73 mounted on the extension 15 and thence under pulley .74 mountedon side plate 14. The end of cable 27 .is wound upon drum 25.

from t p ss ng it wi e .a e P that that.

'5 motor 30 is energized to'rotate the drums 25, 46 in the direction of the arrows indicated, cable 27 will be further wound upon drum 25 and unwound from drum 46 to cause outward extension of the boom section 10, substantially in the manner of the modification'first described. On the other hand, when motor 30 is idle and motor 50 is energized to pivot the boom assembly, for example in clockwise direction about pivot 16, cable 27 functions in the following manner: As the boom assembly is pivoted, pulleys 70 and 73 are moved away from pulley 71. Since the end of cable 27 is anchored about drum 25, the increased distance resulting between said pulleys must be accommodated by forward movement of the cable clamp 28, thereby causing extension of the boom section 10. Cable clamp 28 is permitted to move forwardly by reason of the fact that, during clockwise rota tion of the boom about pivot 16, pulley 68 and drum 46 move closer to pulley 66 to provide the slack in cable 27 needed to permit the cable clamp 28 to move forwardly with the boom section 10. In this manner the work station is moved along a vertical plane automatically as the boom is pivoted on the support 17.

It will' be apparent from the foregoing that, although the boom section 16 may move automatically as the boom assemblyis pivoted about pivot 16, said boom section 10 may also be moved to varying degrees of extension and retraction independently of the angular tilting of the boom assembly by proper manipulation of the push buttons 61 or 63.

A modified system for maintaining the work station horizontal is illustrated in Figure 3, as follows: The levelling cable 39 is secured at it forward end to pin 40 mounted on the work station 37, and then extends rearwardly underpulley 41 and through the cable guide 19 and is reeved over pulley 76 mounted on side plate 14. Cable 39 then extends downwardly. under pulley 77 mounted rotatably on bracket 45, and then upwardly over pulley '78, forwardly through cable guide 19 and around pulley 79 mounted rotatably on the forward end'of the boom sectionll. Cable 39 is then doubled back to extend rearwardly through guide 19, the end of the cable being anchored to clamp 28.

It is to be noted, in the modification of Figure 3, that the levelling cable 39 is anchored firmly at both ends, at

40 and 28, and is not operated by a cable drum, in I contrast with the modification first described. As in the first modification, however, the distances between the points 38 and 40 must be proportioned with respect to the distances between pulleys 76, 78 and pulley 77 to provide automatic levelling of the work station 37 as the boom assembly is pivoted about pivot 16.

The levelling cable 39 performs this levelling function while the boomsection It) is extended and retracted within the :rearwardsection 11 by virtue of the doubled section'of cable extending from pulley 78 to pulley 79 and then back toclamp 28. Thus, as boom section 10 is extended, for example, clamp 28 moves closer to pulley 79, with a corresponding reduction in the length of cable extending between them. The extra cable is thus made available to the resulting additional distance between pulley 76 and terminal connection 40.

:: From the foregoing, it is apparent that the present invention provides extensible booms having features of utility heretofore .not available in conventional boom constructions. The boom assembly is a self-contained unit, with a majority of parts being enclosed therein for protection against wear and damage due to weather and foreign matter. The boom assembly is of sturdy cont struction for efficient'andlon'g operating life, and requires -but"a minimum of maintenance. Although the boom assemblies are illustrated herein as supporting a work station, it will be apparent that the boom may be utilized .in other ways. For example, the terminal end of boom .10 may support a clamping device for gripping a telephone pole, preparatory to installing the latter in the ground.

6 This modification of Figure 3 is. particularly adapted to this use, since the boom end is capable of moving i'n'a vertical plane.

it will be apparent to those skilled in the art that various changes may be made in the details of construction described hereinbefore without departing from the scope and spirit of this invention. Accordingly, it is to be' understood that the foregoing description is primarily il-v lustrative of the invention and is not to be considered as limiting the scope thereof.

Having now described my invention and the manner in which the same may be used, what I claim as new and desired to secure by Letters Patent is:

l. A load handling boom comprising an upstanding support, an elongated hollow rear boom member mounted pivotally on the support, power means interconnecting the support and rear boom member, an elongated holiow forward boom member mounted slidably within the rear boom member for longitudinal movement relative thereto, the forward boom member being open at its rearward end, pulley means mounted on and positioned adjacent the forward end of the rear boom member within the forward boom member, winch means mounted within the rear boom member rearwardly of the forward boom member, cable means mountedon the winch means and extending into the forward boom member through said open rearward end and reeved over said pulley means, means securing the opposite ends of the cable means -to the rearward end of the forward boom member, and reversible power means for driving the winch means to retract and extend the forward boomv member.

2. A load handling boom comprising an upstanding support, an elongated hollow rear boom member mounted pivotally on the support, power'means interconnecting the support and rear boom member, an elongated hollow forward boom member mounted slidably within the rear a ward end, an elongated post secured atits rearward'end to the rear boom member and projecting forwardly into the hollow forward boom member, pulley means mounted on the forward end of the post, winch means mounted within the rear boom member rearwardly of the forward boom member, cable means mounted on thewinch means and extending into theforward 'boom member through said open rearward end and reeved over said pulley means, means securing the opposite ends of the cable means to the rearward end of the forward boom member, and reversible power means for driving the winch means to retract and extend the forward boom member.

3. A load handling boom comprising an upstanding support, an elongated hollow rear boom member mounted pivot'ally on the support, power means interconnecting the'support and rear'boom memberfor pivoting the latter on the support, an elongated hollow forward boom member mounted slidably on the rear boom member for longitudinal movement relative thereto, extensible drive means interconnecting the boom members and operable to extend and retract the forward boom member relative to the rearward boom member, andauxiliary drive means associated with the extensible drivemeans and interconnecting the rear boom member and the support, the auxiliary drive means being operable by angular rotation of the rear boom member relative to'the support to extend and retract the forward end of the forward boom member along a substantially straight line during pivotal movement of the rear boom member.

4. A load handling boom comprising an upstanding support, an elongated hollow rear boom membermounted pivotaily on the support, power means interconnecting 5. A load handling boom comprising an upstanding support, an' elongated hollow rear boom membermounted pivotally on the support, power means interconnecting the support and rear boom member, an elongated hollow forward boom member mounted slidably on the rear boom member for longitudinal movement relative thereto, power means interconnecting the rear and forward boomvmembers for extending and retracting the latter, spaced pulley means mounted on the rearboom member and on the support on opposite sides of the boom pivot, and cable means reeved intermediate its ends over the pulley means on one side of said pivot and thence over the pulley means on the opposite side of the pivot, said pulleys being so' positioned that the forward end of the forward boom member moves along a substantially straight line asthe boom members are pivoted.

.8 work station mounted pivotally on'thezoutefi end of the forward boom member, power means interconnecting the rear and forward boom members for extending andv re: tracting the latter: the combiriationztherewithof first pulley means on the rear boom member, secondipulley ineans'mo'untedon the support, cablemeanssecured at one end to the workstation a spaced distancefrom the pivot mounting of the latter, the cable 'means, being reeved over the firstand second pulleymeans, and means securing the opposite end of the cable means to one of the boom members to accommodate extension and retraction of the cable means simultaneously with the forward boom member, the first and second'pulley means being positionedfor relative displacement as the rear boom member is pivoted on thesupport whereby to extend and retr'actthe forward end of the cable means to maintain the-work support substantiallyhorizontal.

-forward boom member mounted slidably on the rear 6. A load handling boom comprising an upstanding to, pulley means mounted adjacent the forward end of the rear boom-member, winch means on the rear boom member, cable means mounted on the winch'means and reeved over said pulley means, spaced pulley means mounted on the rear boom member andon the support on opposite sides of the boom pivot, the cable means being reeved intermediate-its-ends over the pulley means on one side of said pivot and thence over the' pulley means on the opposite side of the pivot, said pulleys being so positionedthat the forward 'end of theforward boom member moves along a substantially straight line as the boom members are pivoted, means securing the opposite ends of the cable means to the rearward 'end of the forward boom member, and reversible power means for driving the winch means ,to retract and extend the forward boom member. 1 f

7. A load handling boom comprising an upstanding support, "an elongated hollow rear boom member mounted pivotally on the support, power means interconnect ing the support and rear boom member, an elongated hollow forward boom member mounted slidably on the rear boom member for longitudinal movement relative thereto, a post secured to the rear boom member and terminating adjacent the forward end thereof within the hollow forward boom member, pulley means mounted on the forward end of the post, winch rn'eans'on the rear boom member, cable means mounted on the winch means and reeved over said pulley means, spaced pulley means mounted on'the rear boom member ridden the support boom member for longitudinal movement relative thereto, a work station mounted pivotally on the outer end of the forward boom member, powermeans interconnecting the rear and forward boom members for extending and retracting the latter: the combination therewith of first pulley means on the rear boom member, second pulley means mounted on the support, cable means secured at oneend to'the; work station a spaced distance from-the pivot mounting of the latter, the cable means being reeved over thefirst andsecond pulley means, and means securing the opposite end-of the cable means to one of the boom'members to accommodate extension and retraction of the cable; means simultaneously with the forward 'boom member, the distance between'the pivot connection of the work station and the cable means connected thereto I being proportioned with respect to the distance between the second pulley means and the first pulley'mcans and cable securing means .such that their relative displacements during pivoting of the boom members maintains I V the rear and forward boom members for extending and on opposite sides of the boom pivot, cable means reeved intermediate its ends over the pulley means on one side of said pivot and thence over the pulley means on the opposite side of the pivot, said pulleys being so' positioned that the forward end of the forward boom member moves along asubstantially straight line 'as' the boom members are pivoted, means securing the opposite ends of the cable means to the rearward end of the forward boommemben-reversible power means for driving the winch means to retract and extend the forward boom member. b b

8. In a load handling boom including an upstanding support, an elongated hollow rear boom member mounted pivotally on the support, power means interconnecting the support and rear boom member, an elongated hollow forward boom'member mounted slidably on the rear boom member for longitudinal movement relative thereto, a r

retracting the latter: the combination'therewith of first pulleymeans on the rearboom'member, second pulley means mounted on the support, cable means secured at oneend to the work station a spaced distance from the pivot mounting of the latter, the cable means being reeved over the first :and second pulley means, and third and fourth pulley means mounted on the rear boom member adjacent the rear and forward ends respectivelyiof the latter, the cable means being'reeved forwardly over the third and fourth pulley meansand thence re'arwardly for attachment at its opposite end to the rearward end of the a forward boom lmember.

111; A-load handling boom comprisingfan upstanding "support, an elongated hollow rear boom member mounted pivotally on the support, power-means interconnectingth'e support and rear boom member, an elongated hollow forward'boom member mounted slidably on the rear boom member for longitudinal movement relative thereto, a j work station'mounted pivotally on the outer end of the forward boom member, pulley means mounted adjacent the forward end of the rear boom member, winch means on the rear boom member, cable means mounted on the winchmeans and reeved over said pulley means, means securing the opposite ends-of the-cable means to the rearward end of the forward boom member, reversible power means for driving the winch means to retract and extend the forward boom member, second pulley means on the rear boom member, third pulley means mounted on the Support, second cable means secured at one end to the work station a spaced distance from the pivot mounting of the latter, the second cable means being reeved over the second and third pulley means, and second winch means mounted on the rear boom member for securing the opposite end of the second cable means thereto, the second winch means being operable simultaneously with the first winch means.

12. A load handling boom comprising an upstanding support, an elongated hollow rear boom member mounted pivotally on the support, power means interconnecting the support and rear boom member, an elongated hollow forward boom member mounted slidably on the rear boom member for longitudinal movement relative thereto, a work station mounted pivotally on the outer end of the forward boom member, a post secured to the rear boom member and terminating adjacent the forward end thereof within the hollow forward boom member, pulley means mounted on the forward end of the post, winch means on the rear boom member, cable means mounted on the winch means and reeved over said pulley means, means securing the opposite ends of the cable means to the rearward end of the forward boom member, reversible power means for driving the winch means to retract and extend the forward boom member, and power means interconnecting the boom members and support and responsive to the longitudinal movement and angular rotation of the boom members with respect to said support to maintain the work station substantially horizontal.

13. A load handling boom comprising an upstanding support, an elongated hollow rear boom member mounted pivotally on the support, power means interconnecting the support and rear boommember, an elongated hollow forward boom member mounted slidably on the rear boom member for longitudinal movement relative thereto, a work station mounted pivotally on the outer end of the forward boom member, a post secured to the rear boom member and terminating adjacent the forward end thereof within the hollow forward boom member, pulley means mounted on the forward end of the post, winch means on the rear boom member, cable means mounted on the winch means and reeved over said pulley means, means securing the opposite ends of the cable means to the rearward end of the forward boom member, reversible power means for driving the winch means to retract and extend the forward boom member, second pulley means 7 on the rear boom member, third pulley means mounted on the support, second cable means secured at one end to the work station a spaced distance from the pivot mounting of the latter, the second cable means being reeved over the second and third pulley means, and second winch means mounted on the rear boom member for securing the opposite end of the second cable means thereto, the second winch means being operable simultaneously with the first winch means.

14. A load handling boom comprising an upstanding support, an elongated hollow rear boom member mounted pivotally on the support, power means interconnecting the support and rear boom member, an elongated hollow forward boom member mounted slidably on the rear boom member for longitudinal movement relative thereto, a work station mounted pivotally on the outer end of the forward boom member, power means interconnecting the rear and forward boom members for extending and re tracting the latter, power means interconnecting the boom members and support and responsive to the angular rotation of the boom members with respect to said support'to extend and retract the forward boom member such that the forward end of the forward boom member moves along a substantially straight line as the boom members are pivoted, first pulley means on the rear boom member,

second pulley means mounted on the support, cable means secured at one end to the work station a spaced distance from the pivot mountingof the latter, the'cable means being reeved over the first and second pulley means, and means securing the opposite end of the cable means to one of the boom members to accommodate extension and retraction of the cable means simultaneously with the forward boom member.

15. A load handling boom comprising an upstanding support, an elongated hollow rear boom member mounted pivotally on the support, power means interconnecting the support and rear boom member, an elongated hollow forward boom member mounted slidably on the rear boom member for longitudinal movement relative thereto, a work station mounted pivotally on the outer end of the forward boom member, power means interconnecting the rear and forward boom members for extending and re-' tracting the'latter, spaced pulley means mounted on the rear boom member and on the support on opposite sides of the boom pivot, cable means reeved intermediate its ends over the pulley means on one side of said pivot and thence over the pulley means on the opposite side'of the pivot, said pulleys being so positioned that the forward end of'the forward boom member moves along a substantially straight line as the boom members are pivoted, second pulley means on the rear boom member, third pulley means mounted on the support, second cable means secured at one end to the work station a spaced distance from the pivot mounting of the latter, the second cable means being reeved over the second and third pulley means, and means securing the opposite end of the second cable means to one of the boom members to accommodate extension and retraction of the cable means simultaneously with the forward boom member.

support, an elongated hollow rear boom member mounted pivotally on the support, power means interconnecting the support and rear boom member, an elongated hollow forward boom member mounted slidably on the rear boom member for longitudinal movement relative thereto, a work station mounted pivotally on the outer end of the forward boom member, a post secured to the rear boom member and terminatingadjacent the forward end thereof within the hollow forward boom member, pulley means mounted on the forward end of the post, winch means on the rear boom member, first cable means mounted on the winch means and reeved over said pulley means, means securing the first cable means to the rearward end of the forward boom member, reversible power means for driving the winch means to retract and extend the forward boom member, second cable means interconnecting the a power means interconnecting the boom members and.

support and responsive to the angular rotation of the boom members with respect to said support to extend and retract the forward boom member such that the forward end of the forward boom member moves along a substantially straight line as the boom members are pivoted.

17. A load handling boom comprising an upstanding support, an elongated rear boom member mounted pivotally on the support, power means interconnecting the support and rear boom member for pivoting the latter on the support, an elongated forward boom member mounted on the rear boom member for movement relative thereto, extensible drive means interconnecting the boom members and operable to extend and retract the forward boom member relative to the rearward boom member, and auxiliary drive means associated with the extensible drive means and interconnecting the rear boom member and the support, the auxiliary drive means being operable by angular rotation of the rear boom member relative to the support to extend and retract the forward boom member automatically-to causga 'movemgnt of -the forward end of the forward bpom member along a substantially straight line during pivotal movement of the rear boom member.

r R efei-ence s Cit ed iu the file of this patent V w UNITED STATES PATENTS 1,345,304 Zied June 9, 1920 Strauss Aug. 26, 1924 Honig May 29, 1945 -Wi1son et a1 Mar. 1, 1949 Schmidt Aug. 18, 1953 Schmidt June 29, 1954 Qldcnkamp July 20, 1954 Harsch- Mar. 26, 1957 Autos et a1 Apr. 2, 1957 

